The chalk lined tunnel - actually recently relined in concrete) between Higham station and Strood Station was the longest chalk-lined tunnel in Europe - but for the old chalk workings in the middle of it which cut it in half. I know where those chalk workings can be found from overground, but I don't know of any safe access. I think they were Roman or even pre-Roman. The recent re-lining was because of increasingly frequent chalk falls, that were disrupting train services.

The tunnel was originally dug for the Thames and Medway Canal, and it was a "walk-through" tunnel - the men lay on their backs on the cabin of the barges and walked their feet along the tunnel roof, to propel the barges through. The railway company bought the tunnel off the canal company. and filled that bit of the canal in, although a fair bit of water still goes down the tunnel to Strood.

Quite a fair bit of the canal has vanished over the years although the canal basin in Gravesend has only recently started the process of gentrification.   


THere used to be a tunnel from Gads Hill House to Gads Hill School under the A226 - filled in with concrete some years ago.

THere used to be a tunnel from the Rose and Crown in All Hallows to the church under the Stoke Road - filled in with concrete some years ago.


There used to be tunnels from Grain to the Martello towers. Guess what? Yes, concrete!


Threre have been reputed to be smugglers tunnels around All Hallows and the Yantlet since the days of "the Gentlemen" (although the "Gentlemen" were elsewhere) and although there were tales of children going missing I think the smart money is on those tunnels having been ploughed in long since. If you dig too deep near Allhallows you get a spring, not a tunnel!


There are undoubtedly tunnels below Rochester Castle, my late wife went down them as a child on guided tours, but along with the other dpradations of English Heritage at Rochester Castle the tunnels have been closed.


There is supposed to be a tunnel from the cellars of the Coopers Arms to Rochester Castle - or maybe to the Cathedral.


Tere is undoubedly a tunnel complex under Beacon Hill, Chattenden - but don't try for it, it is in active MoD use for a radio network that transmits signals to nuclear submarines...